Field effect transistors with reduced gate fringe area and method of making the same

ABSTRACT

A semiconductor structure includes at least two field effect transistors. A gate strip including a plurality of gate dielectrics and a gate electrode strip can be formed over a plurality of semiconductor active regions. Source/drain implantation is conducted using the gate strip as a mask. The gate strip is divided into gate electrodes after the implantation.

FIELD

The present disclosure relates generally to the field of semiconductordevices and specifically to field effect transistors with reduced gatefringe area and methods of making the same.

BACKGROUND

Prior art high voltage field effect transistors often suffer fromsurface breakdown voltage. Such transistors often have a complexextended low doped drain (LDD) structure to improve surface breakdowncharacteristics at the expense of process complexity and increased cost.

SUMMARY

According to an aspect of the present disclosure, a semiconductorstructure comprises first and second field effect transistors and ashallow trench isolation structure. Each of the first and second fieldeffect transistors comprises a semiconductor active region including asource region, a channel region, and a drain region arranged along afirst horizontal direction, a gate dielectric contacting a top surfaceof the channel region, a gate electrode overlying the gate dielectric,and a dielectric gate spacer laterally surrounding the gate electrode.The shallow trench isolation structure laterally surrounds each of thesemiconductor active regions of the first and second two field effecttransistors. The shallow trench isolation structure has a planar topsurface between two via cavities extending in the first horizontaldirection and located in an inter-gate region between the gateelectrodes of the first and second field effect transistors, and thedielectric gate spacers of the first and the second field effecttransistors contain downward-protruding portions which fill the two viacavities in the shallow trench isolation structure.

According to another aspect of the present disclosure, a field effecttransistor comprises a semiconductor active region including a sourceregion, a channel region, and a drain region arranged along a firsthorizontal direction, a gate dielectric contacting a top surface of thechannel region, a gate electrode having four sides overlying the gatedielectric, a dielectric gate spacer laterally surrounding the gateelectrode on the four sides, and dielectric offset spacers located onlyon two sides of the gate electrode which extend in a second horizontaldirection which is perpendicular to the first horizontal direction. Thegate dielectric spacers physically contact the dielectric offset spacersover the two sides of the gate electrode which extend in the secondhorizontal direction, and the gate dielectric spacers physically contactanother two sides of the gate electrode which extend in the firsthorizontal direction.

According to another aspect of the present disclosure, a method offorming a semiconductor device comprises forming a shallow trenchisolation structure in an upper region of a semiconductor substrate thathas a doping of a first conductivity type, wherein the shallow trenchisolation structure laterally surrounds a plurality of semiconductoractive regions that are patterned portions of the semiconductorsubstrate, have lengthwise edges that are parallel to a first horizontaldirection, and are laterally spaced apart along a second horizontaldirection that is perpendicular to the first horizontal direction,forming a gate strip comprising a vertical stack of a plurality of gatedielectrics and a gate electrode strip over the plurality ofsemiconductor active regions, wherein the gate strip continuouslyextends as a single continuous structure over each of the plurality ofsemiconductor active regions and over portions of the shallow trenchisolation structure located between the plurality of semiconductoractive regions, forming source/drain extension regions by implantingdopants of a second conductivity type into surface portions of theplurality of semiconductor active regions that are not masked by thegate strip after formation of the gate strip, and dividing the gatestrip into the gate stacks by removing portions of the gate strip thatare located within areas of the shallow trench isolation structure afterforming the source/drain extension regions.

According to yet another aspect of the present disclosure, asemiconductor structure comprises first and second field effecttransistors and a shallow trench isolation structure. Each of the firstand second field effect transistors comprises a semiconductor activeregion including a source region, a channel region, and a drain regionarranged along a first horizontal direction, a gate dielectriccontacting a top surface of the channel region, a gate electrodeoverlying the gate dielectric, and a pair of dielectric gate spacerslocated on opposite sides of the gate electrode. The shallow trenchisolation structure laterally surrounds each of the semiconductor activeregions of the first and second two field effect transistors. Each ofthe pair of dielectric gate spacers comprises over-active-region gatespacer portions overlying the semiconductor active regions andcomprising straight inner sidewalls that are perpendicular to the firsthorizontal direction; and inter-active-region gate spacer portionsoverlying portions of the shallow trench isolation structure andcomprising stepped sidewalls including a lower straight sidewall segmentadjoined to a respective pair of straight inner sidewalls, an upperstraight sidewall segment that is laterally offset from the lowerstraight sidewall segment, and a connecting surface that is adjoined toa top edge of the lower straight sidewall segment and to a bottom edgeof the upper straight sidewall segment.

According to still another aspect of the present disclosure, a method offorming a semiconductor device is provided, which comprises: forming ashallow trench isolation structure in an upper region of a semiconductorsubstrate that has a doping of a first conductivity type, wherein theshallow trench isolation structure laterally surrounds a plurality ofsemiconductor active regions that are patterned portions of thesemiconductor substrate, have lengthwise edges that are parallel to afirst horizontal direction, and are laterally spaced apart along asecond horizontal direction that is perpendicular to the firsthorizontal direction; forming a gate strip over the plurality ofsemiconductor active regions, wherein the gate strip comprises aplurality of gate dielectrics and a gate electrode strip; forming adielectric gate spacer around the gate strip; forming deep source/drainregions by implanting dopants of a second conductivity type that is anopposite of the first conductivity type into portions of the pluralityof semiconductor active regions that are not masked by the gate stripand the dielectric gate spacer; and dividing the gate electrode stripinto a plurality of gate electrodes that are laterally spaced apartalong the second horizontal direction and overlies a respective one ofthe plurality of semiconductor active regions after forming the deepsource/drain regions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a vertical cross-sectional view of a first exemplarystructure after formation of a gate dielectric layer, a semiconductorgate electrode material layer, a silicon oxide capping layer, and asilicon nitride capping layer according to an embodiment of the presentdisclosure.

FIG. 1B is a top-down view of the first exemplary structure of FIG. 1A.The vertical plane A-A′ is the plane of the vertical cross-section ofFIG. 1A.

FIG. 2A is a vertical cross-sectional view of the first exemplarystructure after formation of shallow trenches according to an embodimentof the present disclosure.

FIG. 2B is a top-down view of the first exemplary structure of FIG. 2A.The vertical plane A-A′ is the plane of the vertical cross-section ofFIG. 2A.

FIG. 3A is a vertical cross-sectional view of the first exemplarystructure after deposition of a dielectric fill material layer accordingto an embodiment of the present disclosure.

FIG. 3B is a top-down view of the first exemplary structure of FIG. 3A.The vertical plane A-A′ is the plane of the vertical cross-section ofFIG. 3A.

FIG. 4A is a vertical cross-sectional view of the first exemplarystructure after deposition of a shallow trench isolation structureaccording to an embodiment of the present disclosure.

FIG. 4B is a top-down view of the first exemplary structure of FIG. 4A.The vertical plane A-A′ is the plane of the vertical cross-section ofFIG. 4A.

FIG. 5A is a vertical cross-sectional view of the first exemplarystructure after removal of the silicon nitride capping layer and thesilicon oxide capping layer according to an embodiment of the presentdisclosure.

FIG. 5B is a top-down view of the first exemplary structure of FIG. 5A.The vertical plane A-A′ is the plane of the vertical cross-section ofFIG. 5A.

FIG. 6A is a vertical cross-sectional view of the first exemplarystructure after formation of a metallic gate electrode material layerand a gate cap dielectric layer according to an embodiment of thepresent disclosure.

FIG. 6B is a top-down view of the first exemplary structure of FIG. 6A.The vertical plane A-A′ is the plane of the vertical cross-section ofFIG. 6A.

FIG. 7A is a vertical cross-sectional view of the first exemplarystructure after formation of a gate strip according to an embodiment ofthe present disclosure.

FIG. 7B is a top-down view of the first exemplary structure of FIG. 7A.The vertical plane A-A′ is the plane of the vertical cross-section ofFIG. 7A.

FIG. 7C is a vertical cross-sectional view of the first exemplarystructure along the vertical plane C-C′ of FIG. 7B.

FIG. 7D is a vertical cross-sectional view of the first exemplarystructure along the vertical plane D-D′ of FIG. 7B.

FIG. 8A is a vertical cross-sectional view of the first exemplarystructure after formation of an offset spacer and source/drain extensionregions according to an embodiment of the present disclosure.

FIG. 8B is a top-down view of the first exemplary structure of FIG. 8A.The vertical plane A-A′ is the plane of the vertical cross-section ofFIG. 8A.

FIG. 8C is a vertical cross-sectional view of the first exemplarystructure along the vertical plane C-C′ of FIG. 8B.

FIG. 8D is a vertical cross-sectional view of the first exemplarystructure along the vertical plane D-D′ of FIG. 8B.

FIG. 9A is a vertical cross-sectional view of the first exemplarystructure after application and patterning of a photoresist layeraccording to an embodiment of the present disclosure.

FIG. 9B is a top-down view of the first exemplary structure of FIG. 9A.The vertical plane A-A′ is the plane of the vertical cross-section ofFIG. 9A.

FIG. 9C is a vertical cross-sectional view of the first exemplarystructure along the vertical plane C-C′ of FIG. 9B.

FIG. 9D is a vertical cross-sectional view of the first exemplarystructure along the vertical plane D-D′ of FIG. 9B.

FIG. 10A is a vertical cross-sectional view of the first exemplarystructure after patterning the gate strip into gate stacks according toan embodiment of the present disclosure.

FIG. 10B is a top-down view of the first exemplary structure of FIG.10A. The vertical plane A-A′ is the plane of the vertical cross-sectionof FIG. 10A.

FIG. 10C is a vertical cross-sectional view of the first exemplarystructure along the vertical plane C-C′ of FIG. 10B.

FIG. 10D is a vertical cross-sectional view of the first exemplarystructure along the vertical plane D-D′ of FIG. 10B.

FIG. 11A is a vertical cross-sectional view of the first exemplarystructure after formation of dielectric gate spacers according to anembodiment of the present disclosure.

FIG. 11B is a top-down view of the first exemplary structure of FIG.11A. The vertical plane A-A′ is the plane of the vertical cross-sectionof FIG. 11A.

FIG. 11C is a vertical cross-sectional view of the first exemplarystructure along the vertical plane C-C′ of FIG. 11B.

FIG. 11D is a vertical cross-sectional view of the first exemplarystructure along the vertical plane D-D′ of FIG. 11B.

FIG. 12A is a vertical cross-sectional view of the first exemplarystructure after formation of deep source/drain regions according to anembodiment of the present disclosure.

FIG. 12B is a top-down view of the first exemplary structure of FIG.12A. The vertical plane A-A′ is the plane of the vertical cross-sectionof FIG. 12A.

FIG. 12C is a vertical cross-sectional view of the first exemplarystructure along the vertical plane C-C′ of FIG. 12B.

FIG. 12D is a vertical cross-sectional view of the first exemplarystructure along the vertical plane D-D′ of FIG. 12B.

FIG. 13A is a vertical cross-sectional view of the first exemplarystructure after formation of dielectric liners and a contact-leveldielectric layer according to an embodiment of the present disclosure.

FIG. 13B is a top-down view of the first exemplary structure of FIG.13A. The vertical plane A-A′ is the plane of the vertical cross-sectionof FIG. 13A.

FIG. 13C is a vertical cross-sectional view of the first exemplarystructure along the vertical plane C-C′ of FIG. 13B.

FIG. 13D is a vertical cross-sectional view of the first exemplarystructure along the vertical plane D-D′ of FIG. 13B.

FIG. 14A is a vertical cross-sectional view of the first exemplarystructure after formation of contact via structures according to anembodiment of the present disclosure.

FIG. 14B is a top-down view of the first exemplary structure of FIG.14A. The vertical plane A-A′ is the plane of the vertical cross-sectionof FIG. 14A.

FIG. 14C is a vertical cross-sectional view of the first exemplarystructure along the vertical plane C-C′ of FIG. 14B.

FIG. 14D is a vertical cross-sectional view of the first exemplarystructure along the vertical plane D-D′ of FIG. 14B.

FIG. 15A is a vertical cross-sectional view of a second exemplarystructure after formation of a dielectric gate spacer according to anembodiment of the present disclosure.

FIG. 15B is a top-down view of the second exemplary structure of FIG.15A. The vertical plane A-A′ is the plane of the vertical cross-sectionof FIG. 15A.

FIG. 15C is a vertical cross-sectional view of the second exemplarystructure along the vertical plane C-C′ of FIG. 15B.

FIG. 15D is a vertical cross-sectional view of the second exemplarystructure along the vertical plane D-D′ of FIG. 15B.

FIG. 16A is a vertical cross-sectional view of the second exemplarystructure after formation of deep source/drain regions according to anembodiment of the present disclosure.

FIG. 16B is a top-down view of the second exemplary structure of FIG.16A. The vertical plane A-A′ is the plane of the vertical cross-sectionof FIG. 16A.

FIG. 16C is a vertical cross-sectional view of the second exemplarystructure along the vertical plane C-C′ of FIG. 16B.

FIG. 16D is a vertical cross-sectional view of the second exemplarystructure along the vertical plane D-D′ of FIG. 16B.

FIG. 17A is a vertical cross-sectional view of the second exemplarystructure after application and patterning of a photoresist layeraccording to an embodiment of the present disclosure.

FIG. 17B is a top-down view of the second exemplary structure of FIG.17A. The vertical plane A-A′ is the plane of the vertical cross-sectionof FIG. 17A.

FIG. 17C is a vertical cross-sectional view of the second exemplarystructure along the vertical plane C-C′ of FIG. 17B.

FIG. 17D is a vertical cross-sectional view of the second exemplarystructure along the vertical plane D-D′ of FIG. 17B.

FIG. 18A is a vertical cross-sectional view of the second exemplarystructure after patterning the gate strip into gate stacks according toan embodiment of the present disclosure.

FIG. 18B is a top-down view of the second exemplary structure of FIG.18A. The vertical plane A-A′ is the plane of the vertical cross-sectionof FIG. 18A.

FIG. 18C is a vertical cross-sectional view of the second exemplarystructure along the vertical plane C-C′ of FIG. 18B.

FIG. 18D is a vertical cross-sectional view of the second exemplarystructure along the vertical plane D-D′ of FIG. 18B.

FIG. 19A is a vertical cross-sectional view of the second exemplarystructure after removal of the photoresist layer according to anembodiment of the present disclosure.

FIG. 19B is a top-down view of the second exemplary structure of FIG.19A. The vertical plane A-A′ is the plane of the vertical cross-sectionof FIG. 19A.

FIG. 19C is a vertical cross-sectional view of the second exemplarystructure along the vertical plane C-C′ of FIG. 19B.

FIG. 19D is a vertical cross-sectional view of the second exemplarystructure along the vertical plane D-D′ of FIG. 19B.

FIG. 19E is a vertical cross-sectional view of the second exemplarystructure along the vertical plane E-E′ of FIG. 19B.

FIG. 20A is a vertical cross-sectional view of the second exemplarystructure after formation of dielectric liners, a contact-leveldielectric layer, and contact via structures according to an embodimentof the present disclosure.

FIG. 20B is a top-down view of the second exemplary structure of FIG.20A. The vertical plane A-A′ is the plane of the vertical cross-sectionof FIG. 20A.

FIG. 20C is a vertical cross-sectional view of the second exemplarystructure along the vertical plane C-C′ of FIG. 20B.

FIG. 20D is a vertical cross-sectional view of the second exemplarystructure along the vertical plane D-D′ of FIG. 20B.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed to field effecttransistors with reduced gate fringe area and methods of making thesame, the various aspects of which are now described in detail.

The drawings are not drawn to scale. Multiple instances of an elementmay be duplicated where a single instance of the element is illustrated,unless absence of duplication of elements is expressly described orclearly indicated otherwise. Ordinals such as “first,” “second,” and“third” are employed merely to identify similar elements, and differentordinals may be employed across the specification and the claims of theinstant disclosure. The term “at least one” element refers to allpossibilities including the possibility of a single element and thepossibility of multiple elements.

The same reference numerals refer to the same element or similarelement. Unless otherwise indicated, elements having the same referencenumerals are presumed to have the same composition and the samefunction. Unless otherwise indicated, a “contact” between elementsrefers to a direct contact between elements that provides an edge or asurface shared by the elements. If two or more elements are not indirect contact with each other or among one another, the two elementsare “disjoined from” each other or “disjoined among” one another. Asused herein, a first element located “on” a second element can belocated on the exterior side of a surface of the second element or onthe interior side of the second element. As used herein, a first elementis located “directly on” a second element if there exist a physicalcontact between a surface of the first element and a surface of thesecond element. As used herein, a first element is “electricallyconnected to” a second element if there exists a conductive pathconsisting of at least one conductive material between the first elementand the second element. As used herein, a “prototype” structure or an“in-process” structure refers to a transient structure that issubsequently modified in the shape or composition of at least onecomponent therein.

As used herein, a “layer” refers to a material portion including aregion having a thickness. A layer may extend over the entirety of anunderlying or overlying structure, or may have an extent less than theextent of an underlying or overlying structure. Further, a layer may bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer may be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer may extend horizontally, vertically, and/or along atapered surface. A substrate may be a layer, may include one or morelayers therein, or may have one or more layer thereupon, thereabove,and/or therebelow.

As used herein, a “layer stack” refers to a stack of layers. As usedherein, a “line” or a “line structure” refers to a layer that has apredominant direction of extension, i.e., having a direction along whichthe layer extends the most.

As used herein, a “semiconducting material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁶ S/cm to 1.0×10⁵ S/cm.As used herein, a “semiconductor material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁶ S/cm to 1.0×10⁵ S/cmin the absence of electrical dopants therein, and is capable ofproducing a doped material having electrical conductivity in a rangefrom 1.0 S/cm to 1.0×10⁵ S/cm upon suitable doping with an electricaldopant. As used herein, an “electrical dopant” refers to a p-type dopantthat adds a hole to a valence band within a band structure, or an n-typedopant that adds an electron to a conduction band within a bandstructure. As used herein, a “conductive material” refers to a materialhaving electrical conductivity greater than 1.0×10⁵ S/cm. As usedherein, an “insulator material”, “insulating material” or a “dielectricmaterial” refers to a material having electrical conductivity less than1.0×10⁻⁶ S/cm. As used herein, a “heavily doped semiconductor material”refers to a semiconductor material that is doped with electrical dopantat a sufficiently high atomic concentration to become a conductivematerial, i.e., to have electrical conductivity greater than 1.0×10⁵S/cm. A “doped semiconductor material” may be a heavily dopedsemiconductor material, or may be a semiconductor material that includeselectrical dopants (i.e., p-type dopants and/or n-type dopants) at aconcentration that provides electrical conductivity in the range from1.0×10⁻⁶ S/cm to 1.0×10⁵ S/cm. An “intrinsic semiconductor material”refers to a semiconductor material that is not doped with electricaldopants. Thus, a semiconductor material may be semiconducting orconductive, and may be an intrinsic semiconductor material or a dopedsemiconductor material. A doped semiconductor material can besemiconducting or conductive depending on the atomic concentration ofelectrical dopants therein. As used herein, a “metallic material” refersto a conductive material including at least one metallic elementtherein. All measurements for electrical conductivities are made at thestandard condition.

As used herein, a “field effect transistor” refers to any semiconductordevice having a semiconductor channel through which electrical currentflows with a current density modulated by an external electrical field.As used herein, a “channel region” refers to a semiconductor region inwhich mobility of charge carriers is affected by an applied electricalfield. A “gate electrode” refers to a conductive material portion thatcontrols electron mobility in the channel region by application of anelectrical field. A “source region” refers to a doped semiconductorregion that supplies charge carriers that flow through the channelregion. A “drain region” refers to a doped semiconductor region thatreceives charge carriers supplied by the source region and passesthrough the channel region. A “source/drain region” refers to a sourceregion of a field effect transistor or a drain region of a field effecttransistor. A “source extension region” refers to a doped semiconductorregion having a lesser dopant concentration than, and having a same typeof doping as, a source region and including a portion disposed betweenthe source region and the channel region. A “drain extension region”refers to a doped semiconductor region having a lesser dopantconcentration than, and having a same type of doping as, a drain regionand including a portion disposed between the drain region and thechannel region. A “source/drain extension region” refers to a sourceextension region or a drain extension region.

Referring to FIGS. 1A and 1B, a first exemplary structure according to afirst embodiment of the present disclosure is illustrated. The firstexemplary structure includes stacks of a gate dielectric layer 50L, asemiconductor gate electrode material layer 52L, a silicon oxide cappinglayer 42, and a silicon nitride capping layer 44 that are formed over asemiconductor substrate 8.

The semiconductor substrate 8 includes a semiconductor material layer10. The semiconductor substrate 8 may optionally include at least oneadditional material layer at a bottom portion thereof. In oneembodiment, the semiconductor substrate 8 can be a bulk semiconductorsubstrate consisting of the semiconductor material layer 10 (e.g.,single crystal silicon wafer), or can be a semiconductor-on-insulator(SOI) substrate including a buried insulator layer (such as a siliconoxide layer) underlying the semiconductor material layer 10, and ahandle substrate underlying the buried insulator layer. Alternatively,the semiconductor material layer 10 may comprise an epitaxialsemiconductor (e.g., single crystal silicon) layer deposited on asemiconductor substrate (e.g., silicon wafer) 8 or may comprise a dopedwell (e.g., doped silicon well) in the upper portions of thesemiconductor substrate (e.g., silicon wafer) 8.

The semiconductor material layer 10 can include a lightly dopedsemiconductor material portion (e.g., silicon portion) on which at leastone field effect transistor can be formed. In one embodiment, theentirety of the semiconductor material in the semiconductor materiallayer 10 may include the lightly doped semiconductor material. Inanother embodiment, the lightly doped semiconductor material can be asemiconductor well embedded within another semiconductor material havinga different dopant concentration and optionally, a doping of theopposite conductivity type. The dopant concentration of the lightlydoped semiconductor material portion may be optimized for a body regionof the at least one field effect transistor to be subsequently formed.For example, the lightly doped semiconductor material portion mayinclude electrical dopants at an atomic concentration in a range from1.0×10¹⁴/cm³ to 1.0×10¹⁸/cm³, such as from 1.0×10¹⁵/cm³ to 1.0×10¹⁷/cm³,although lesser and greater atomic concentrations can also be employed.The conductivity type of the portion of the semiconductor material layer10 to be subsequently employed as a body region of a field effecttransistor is herein referred to as a first conductivity type, which maybe p-type for an n-type field effect transistor or n-type for a p-typefield effect transistor.

The semiconductor material of the semiconductor material layer 10 can bean elemental semiconductor material (such as silicon) or an alloy of atleast two elemental semiconductor materials (such as a silicon-germaniumalloy), or can be a compound semiconductor material (such as a III-Vcompound semiconductor material or a II-VI compound semiconductormaterial), or can be an organic semiconductor material. The thickness ofthe semiconductor material layer 10 can be in a range from 0.5 mm to 2mm in case the semiconductor material layer 10 is a bulk semiconductorsubstrate. In case the semiconductor material layer 10 is asemiconductor-on-insulator substrate, the thickness of the topsemiconductor material layer within the semiconductor material layer 10may be in a range from 100 nm to 1,000 nm, although lesser and greaterthicknesses can also be employed.

The gate dielectric layer 50L, the semiconductor gate electrode materiallayer 52L, the silicon oxide capping layer 42, and the silicon nitridecapping layer 44 can be sequentially deposited over the semiconductorsubstrate 8.

The gate dielectric layer 50L includes a dielectric material having athickness suitable for operation of a high voltage field effecttransistor. The gate dielectric layer 50L can be conformally formed onall physically exposed surfaces of the semiconductor material layer 10,for example, by thermal oxidation of the physically exposed surfaceportions of the semiconductor material layer 10. If the semiconductormaterial layer 10 includes single crystalline silicon, the gatedielectric layer can consist essentially of thermal silicon oxide. Inone embodiment, the gate dielectric layer 50L may consist essentially ofa semiconductor oxide of a material of the semiconductor substrate 8,and may have the same thickness throughout. The thickness of the gatedielectric layer 50L can be in a range from 6 nm to 100 nm, such as from10 nm to 60 nm, although lesser and greater thicknesses can also beemployed.

The semiconductor gate electrode material layer 52L includes a dopedsemiconductor material such as doped polysilicon. The semiconductor gateelectrode material layer 52L can be deposited over the gate dielectriclayer 50L. For example, the semiconductor gate electrode material layer52L can be deposited by chemical vapor deposition (CVD). The thicknessof the semiconductor gate electrode material layer 52L can be in a rangefrom 30 nm to 300 nm, although lesser and greater thicknesses may alsobe employed.

The silicon oxide capping layer 42 comprises a silicon oxide materialsuch as undoped silicate glass. The silicon oxide capping layer 42 maybe deposited, for example, by chemical vapor deposition. The thicknessof the silicon oxide capping layer 42 may be in a range from 10 nm to100 nm, although lesser and greater thicknesses may also be employed.

The silicon nitride capping layer 44 comprises silicon nitride. Thesilicon nitride capping layer 44 may be deposited, for example, bychemical vapor deposition. The thickness of the silicon nitride cappinglayer 44 may be in a range from 30 nm to 300 nm, although lesser andgreater thicknesses may also be employed.

Referring to FIGS. 2A and 2B, a photoresist layer 17 can be applied overthe first exemplary structure, and can be lithographically patternedinto discrete photoresist material portions that overlie the area of arespective transistor active region 10A. Each transistor active region10A includes the area of a respective combination of a source region, achannel region, and a drain region of a respective field effecttransistor to be subsequently formed. The transistor active regions 10Aare also referred to as semiconductor active regions.

An anisotropic etch process can be performed to etch shallow trenches 19that vertically extend through the silicon nitride capping layer 44, thesilicon oxide capping layer 42, the semiconductor gate electrodematerial layer 52L, and the gate dielectric layer 50L, and into an upperportion of the semiconductor material layer 10. The photoresist layer 17can be employed as an etch mask layer during the anisotropic etchprocess. The depth of the shallow trenches 19, as measured from thehorizontal plane including the top surface of the semiconductor materiallayer 10, can be in a range from 100 nm to 2,000 nm, such as from 200 nmto 1,000 nm, although lesser and greater depths may also be employed.

The shallow trenches 19 can be interconnected with each other. Theshallow trenches 19 laterally surround each of the transistor activeregions 10A. The transistor active regions 10A are portions of thesemiconductor material layer 10 that are located above the horizontalplane including the bottom surfaces of the shallow trenches 19 andlaterally surrounded by a continuous set of sidewalls of the shallowtrenches 19. In other words, each unetched portion of the semiconductormaterial layer 10 laterally surrounded by the shallow trenches 19constitutes a transistor active region 10A. The photoresist layer 17 canbe subsequently removed, for example, by ashing.

Referring to FIGS. 3A and 3B, at least one dielectric fill material canbe deposited in the shallow trenches 19 to form a dielectric fillmaterial layer 20L. The at least one dielectric fill material mayinclude undoped silicate glass. The at least one dielectric fillmaterial may be deposited by a conformal deposition process such as achemical vapor deposition process.

Referring to FIGS. 4A and 4B, a chemical mechanical planarizationprocess can be performed to remove portions of the dielectric fillmaterial layer 20L from above the horizontal plane including the topsurfaces of the silicon nitride capping layer 44. Remaining portions ofthe dielectric fill material layer 20L constitute a shallow trenchisolation structure 20. The shallow trench isolation structure 20 can besubsequently vertically recessed so that the top surface of the shallowtrench isolation structure 20 are formed about the horizontal planeincluding the bottom surfaces of the silicon nitride capping layer 44.

Referring to FIGS. 5A and 5B, the silicon nitride capping layer 44 canbe removed selective to the shallow trench isolation structure 20 andthe silicon oxide capping layer 42. For example, a wet etch processemploying hot phosphoric acid can be performed to remove the siliconnitride capping layer 44. Subsequently, an etch process that etches thesilicon oxide material of the silicon oxide capping layer 42 can beperformed to remove the silicon oxide capping layer 42 selective to thematerials of the semiconductor gate electrode material layer 52L. In oneembodiment, the etch process may comprise a wet etch process employingdilute hydrofluoric acid. The top surface of the shallow trenchisolation structure 20 can be collaterally vertically recessed duringthe etch process. In one embodiment, the top surface of the shallowtrench isolation structure 20 can be located about the height of the topsurfaces of the semiconductor gate electrode material layer 52L. Theshallow trench isolation structure 20 can be formed through thesemiconductor gate electrode material layer 52L and the gate dielectriclayer 50L and into an upper portion of the semiconductor substrate 8.

Generally, a shallow trench isolation structure 20 can be formed in anupper region of a semiconductor substrate 8 that has a doping of a firstconductivity type. The shallow trench isolation structure 20 laterallysurrounds a plurality of transistor active regions 10A that arepatterned portions of the semiconductor substrate 8, have lengthwiseedges that are parallel to a first horizontal direction hd1, and arelaterally spaced apart along a second horizontal direction hd2 that isperpendicular to the first horizontal direction hd1. In one embodiment,the shallow trench isolation structure 20 laterally surrounds each ofthe semiconductor active regions 10A of at least two field effecttransistors that are arranged along the second horizontal direction hd2.In one embodiment, the shallow trench isolation structure 20 can have aplanar top surface located in a horizontal plane.

Referring to FIGS. 6A and 6B, a metallic gate electrode material layer54L can be deposited directly on top surfaces of the semiconductor gateelectrode material layer 52L. The metallic gate electrode material layer54L comprises metallic material such as a transition metal, a conductivemetallic nitride material (such as TiN, TaN, or WN), or metal silicidematerial. The metallic gate electrode material layer 54L may bedeposited by physical vapor deposition and/or chemical vapor deposition.The metallic gate electrode material layer 54L can have a thickness in arange from 50 nm to 150 nm, although lesser and greater thicknesses mayalso be employed.

A gate cap dielectric layer 58L can be subsequently deposited over themetallic gate electrode material layer 54L. The gate cap dielectriclayer 58L can include a passivation dielectric material such as siliconnitride. The gate cap dielectric layer 58L can be deposited, forexample, by chemical vapor deposition. The thickness of the gate capdielectric layer 58L can be in a range from 10 nm to 100 nm, such asfrom 20 nm to 60 nm, although lesser and greater thicknesses may also beemployed.

Referring to FIGS. 7A-7D, a photoresist layer (not shown) can be appliedover the gate cap dielectric layer 58L, and can be patterned intodiscrete photoresist material portions by lithographic exposure anddevelopment. Each patterned photoresist material portion can have ashape of a respective gate strip to be subsequently formed. In oneembodiment, the transistor active regions 10A may be arranged as atleast one row of transistor active regions 10A arranged along the secondhorizontal direction hd2. In one embodiment, the transistor activeregions 10A may be arranged as multiple rows of transistor activeregions 10A arranged along the second horizontal direction hd2. In thiscase, the illustrated portion of the first exemplary structure as shownin FIGS. 7A-7D corresponds to two neighboring transistor active regions10A that are arranged along the second horizontal direction hd2. In oneembodiment, the transistor active regions 10A may be arranged as atwo-dimensional periodic array such as a two-dimensional periodicrectangular array.

Each patterned photoresist material portion can may have a respectiverectangular horizontal cross-sectional shape having a respective pair oflengthwise sidewalls along the second horizontal direction hd2. In oneembodiment, each patterned photoresist material portion can laterallyextend along the second horizontal direction hd2 over a plurality oftransistor active regions 10A, such as a row of transistor activeregions 10A that are arranged along the second horizontal direction hd2.

An anisotropic etch process can be performed to transfer the pattern ofthe patterned photoresist material portions through the gate capdielectric layer 58L, the metallic gate electrode material layer 54L,the semiconductor gate electrode material layer 52L, and the gatedielectric layer 50L. Unmasked areas of the shallow trench isolationstructure 20 may be collaterally recessed during the anisotropic etchprocess.

A gate strip (50, 52, 54S, 58S) can be formed over each row oftransistor active regions 10A that are arranged along the secondhorizontal direction hd2. Each gate strip (50, 52, 54S, 58S) comprisespatterned portions of the gate cap dielectric layer 58L, the metallicgate electrode material layer 54L, the semiconductor gate electrodematerial layer 52L, and the gate dielectric layer 50L. For example, eachgate strip (50, 52, 54S, 58S) includes a plurality of gate dielectrics50 that are patterned portions of the gate dielectric layer SOL, aplurality of semiconductor gate electrode portions 52 that are patternedportions of the semiconductor gate electrode material layer 52L, ametallic gate electrode strip 54S that is a patterned portion of themetallic gate electrode material layer 54L, and a gate cap dielectricstrip 58S that is a patterned portion of the gate cap dielectric layer58L. A contiguous combination of the plurality of semiconductor gateelectrode portions 52 and the metallic gate electrode strip 54Aconstitutes a gate electrode strip (52, 54S). The gate electrode strip(52, 54S) continuously extends as a single continuous structure overeach transistor active region 10A within a row of transistor activeregions 10A. Each gate electrode strip (52, 54S) can comprise a pair oflengthwise sidewalls that laterally extend along the second horizontaldirection hd2, and laterally spaced apart along the first horizontaldirection by a gate length GL. In one embodiment, each gate electrodestrip (52, 54S) may comprise a plurality of surface segments, such assidewalls of semiconductor gate electrode portions 52, that laterallyextend along the first horizontal direction hd1 and contact a respectivesidewall surface segment of the shallow trench isolation structure 20.

Referring to FIGS. 8A-8D, offset spacers 55 may be optionally formed onsidewalls of the gate strips (50, 52, 54S, 58S). The offset spacers 55may be formed by conformal deposition of a thin dielectric liner and ananisotropic etch process that removes horizontally-extending portions ofthe thin dielectric liner, and/or may be formed by surface oxidation ofthe physically exposed surfaces of the semiconductor gate electrodeportions 52. The lateral thickness of the offset spacer 55, if present,may be in a range from 0.3 nm to 20 nm, such as from 1 nm to 6 nm,although lesser and greater thicknesses may also be employed. The offsetspacers 55 may comprise silicon oxide, silicon nitride or a siliconoxide/silicon nitride bilayer.

Electrical dopants of a second conductivity type can be implanted intounmasked portions of the semiconductor material layer 10 that are notmasked by the gate strips (50, 52, 54S, 58S) to form source/drainextension regions (31, 39). The second conductivity type is the oppositeof the first conductivity type. For example, if the first conductivitytype is p-type, the second conductivity type is n-type, and vice versa.The source/drain extension regions (31, 39) may include, for example,source extension regions 31 and drain extension regions 39. Generally,each of the source/drain extension regions (31, 39) can have a doping ofan opposite conductivity type than the conductivity type of a remainingportion of the transistor active region 10A on which the respective oneof the source/drain extension regions (31, 39) is formed. For example,if a transistor active region 10A has a doping of a first conductivitytype, the source/drain extension regions (31, 39) that are formed withinsurface regions of the transistor active region 10A have a doping of asecond conductivity type that is the opposite of the first conductivitytype. For example, if the first conductivity type is p-type, the secondconductivity type is n-type, and vice versa. The atomic concentration ofdopants in the source/drain extension regions (31, 39) may be in a rangefrom 1.0×10¹⁸/cm³ to 1.0×10²⁰/cm³, although lesser and greater dopantconcentrations may also be employed. Thus, the extension regions (i.e.,LDD regions) (31, 39) are implanted prior to separating the gate strips(50, 52, 54S, 58S) into gate electrodes. The gate strips block the LDDimplant process from doping the edge regions of the transistor activeregions 10A under the gate strips in the gate fringe region. Theprevention of doping the gate fringe regions at the edge of eachtransistor active region 10A doping prevents or reduces a leakagecurrent path through the gate fringe region and reduces the transistorleakage current.

Referring to FIGS. 9A-9D, a photoresist layer 47 can be applied over thefirst exemplary structure, and can be lithographically patterned to formopenings 47A that straddle portions of the gate strips (50, 52, 54S,58S) that overlie top surfaces of the shallow trench isolation structure20. Generally, the patterned photoresist layer 47 can cover the entirearea of each of the transistor active regions 10A, and includesrectangular openings 47A in areas (i.e., the gate fringe areas betweenthe transistor active regions 10A) in which the gate strips (50, 52,54S, 58S) are subsequently cut. In other words, the areas of theopenings 47A in the patterned photoresist layer 47 correspond to thegate fringe areas from which portions of the gate strips (50, 52, 54S,58S) are subsequently removed. In one embodiment, the patternedphotoresist layer comprises a row of openings 47A arranged along thesecond horizontal direction hd2 and located within the gate fringe areasoverlying the shallow trench isolation structure 20 and having an arealoverlap with a respective portion of an underlying gate strip (50, 52,54S, 58S). In one embodiment, a row of rectangular openings 47A can beformed in the patterned photoresist layer 47 over each gate strip (50,52, 54S, 58S).

In one embodiment, each of the rectangular openings 47A in the patternedphotoresist layer 47 can have a pair of first straight sidewalls and apair of second straight sidewalls. The pair of first straight sidewallscan laterally extend along the first horizontal direction hd1 and havinga greater length than the gate length GL (i.e., the lateral dimensionalong the first horizontal direction hd1) of the underlying gate strip(50, 52, 54S, 58S). The pair of second sidewalls can laterally extendalong the second horizontal direction hd2, overlie and contact arespective portion of the shallow trench isolation structure 20, asshown in FIG. 9D. Thus, the second sidewalls do not have an arealoverlap with the underlying gate strip (50, 52, 54S, 58S). The pair ofsecond sidewalls of each opening 47A in the patterned photoresist layer47 also does not have any areal overlap with any of the transistoractive regions 10A.

A portion of the top surface shallow trench isolation structure 20 isexposed in the opening 47A, as shown in FIG. 9D. Specifically, a pair ofrectangular top surface segments of the shallow trench isolationstructure 20 can be physically exposed within the area of each opening47A in the patterned photoresist layer 47. Further, a rectangularsurface segment of the top surface of a gate cap dielectric strip 58Scan be physically exposed within the area of each opening 47A in thepatterned photoresist layer 47. The width of each rectangular opening47A in the patterned photoresist layer 47 along the second horizontaldirection hd2 can be less than the lateral spacing between a neighboringpair of transistor active regions 10A along the second horizontaldirection hd2. The length of each rectangular opening 47A in thepatterned photoresist layer 47 along the first horizontal direction hd1can be greater than the gate length GL of an underlying gate strip (50,52, 54S, 58S), which is the width of the underlying gate strip (50, 52,54S, 58S) along the first horizontal direction hd1.

Referring to FIGS. 10A-10D, an anisotropic etch process can be performedto etch unmasked portions of each gate strip (50, 52, 54S, 58S). Theetch process is performed after implantation of the extension regions(i.e., LDD regions) (31, 39) into the transistor active regions 10A. Thepattern of rows of openings 47A in the patterned photoresist layer 47can be transferred through the gate strips (50, 52, 54S, 58S) and intounmasked areas of the shallow trench isolation structure 20. Unmaskedportions of the offset spacers 55 can be collaterally removed during theanisotropic etch process. Unmasked portions of the shallow trenchisolation structure 20 can be collaterally vertically recessed to formvia cavities 11. A pair of via cavities 11 that vertically extend intothe shallow trench isolation structure 20 can be formed within eachopening within the rows of openings in the patterned photoresist layer47.

Each gate strip (50, 52, 54S, 58S) can be divided into the gate stacks(50, 52, 54, 58) by removing portions of the respective gate strip (50,52, 54S, 58S) that are located within the gate fringe areas overlyingthe shallow trench isolation structure 20. Each gate stack (50, 52, 54,58) includes a vertical stack of a gate dielectric 50, a semiconductorgate electrode portion 52, a metallic gate electrode portion 54, and agate cap dielectric 58. Each metallic gate electrode portion 54 is apatterned portion of a respective metallic gate electrode strip 54S.Each gate cap dielectric 58 is a patterned portion of a gate capdielectric strip 58S. Each of the gate dielectrics 50 is one of aplurality of gate dielectrics 50 within a respective one of the gatestrips (50, 52, 54S, 58S). Each contiguous combination of asemiconductor gate electrode portion 52 and a metallic gate electrodeportion 54 constitutes a gate electrode (52, 54). Thus, each of the gateelectrodes (52, 54) is a patterned portion of a respective gateelectrode strip (52, 54S).

Each gate stack (50, 52, 54, 58) is formed over a respective one of thetransistor active regions 10A. Each gate stack comprises a gatedielectric 50 and a gate electrode (52, 54). In one embodiment, each ofthe gate stacks (50, 52, 54, 58) comprises a pair of peripheral regionsPR located in the gate fringe region and having an areal overlap withthe shallow trench isolation structure 20 in a plan view along avertical direction that is perpendicular to a top surface of thesemiconductor substrate 8.

A pair of via cavities 11 can be formed underneath each opening 47A inthe patterned photoresist layer 47. The pair of via cavities 11comprises a pair of proximal sidewalls 11P that are laterally spacedapart along the first horizontal direction hd1 by a first spacing S1,which is also referred to as a gate spacer inner sidewall spacing, i.e.,the spacing between a pair of inner sidewalls of a gate spacer to besubsequently formed. In one embodiment, the pair of via cavities 11 alsocomprises a pair of distal sidewalls 11D that are laterally spaced apartalong the first horizontal direction hd1 by a second spacing S2, whichis referred to as a trench distal sidewall spacing.

Each region of the shallow trench isolation structure 20 that is locatedwithin an area located between a neighboring pair of gate dielectrics 50is herein referred to as an inter-gate region. Each inter-gate region ofthe shallow trench isolation structure 20 comprises a pair of topmosthorizontal surface segments THSS of the shallow trench isolationstructure 20 that contacts a respective bottom surface segment of aneighboring pair of gate electrodes (52, 54), such as bottom surfacesegments of a neighboring pair of metallic gate electrode portions 54.Further, each inter-gate region of the shallow trench isolationstructure 20 comprises an intermediate horizontal surface segment IHSSthat is adjoined to the topmost horizontal surface segments by a pair ofvertical surface segments and located between a respective pair of viacavities 11. The intermediate horizontal surface segment is physicallyexposed underneath an opening 47A in the patterned photoresist layer 47.

In one embodiment, the intermediate horizontal surface segment IHSS islocated above the horizontal plane including a planar top surface of theshallow trench isolation structure 20 that is covered by the patternedphotoresist layer 47. In one embodiment, bottom surfaces of the viacavities 11 are located below the horizontal plane including the planartop surface of the shallow trench isolation structure 20 that is coveredby the patterned photoresist layer 47.

In one embodiment, each of the via cavities 11 comprises a pair ofstepped proximal sidewalls having a respective horizontal step locatedbetween an upper vertical proximal sidewall segment and a lower verticalproximal sidewall segment. A pair of lower vertical proximal sidewallsegments can be laterally spaced from each other by the first spacingS1. A pair of upper vertical proximal sidewall segments can be laterallyspaced from each other by the gate length GL.

In one embodiment, each of the via cavities 11 comprises a pair of firstsidewalls 111 that are parallel to the first horizontal direction hd1and vertically coincident with widthwise sidewalls of a neighboring pairof gate electrodes (52, 54), and a pair of second sidewalls (such as aproximal sidewall 11P and a distal sidewall 11D) that are perpendicularto the first horizontal direction hd1 and adjoined tovertically-extending edges of the pair of first sidewalls 111. In oneembodiment, each of the gate electrodes (52, 54) comprises a pair oflengthwise sidewalls that is perpendicular to the first horizontaldirection hd1 and laterally spaced apart along the first horizontaldirection hd1 by a gate length GL. In one embodiment, the pair of secondsidewalls 11P of each via cavity 11 comprises a pair of sidewallsegments (which are upper straight sidewall segments of a pair ofstepped sidewalls 11P) that are laterally spaced apart along the firsthorizontal direction by the gate length GL.

In one embodiment, each of the gate electrodes (52, 54) comprises a pairof lengthwise sidewalls that are laterally spaced apart along the firsthorizontal direction hd1 by the gate length GL and laterally extendalong the second horizontal direction hd2. A lateral spacing between apair of horizontal steps 11H of the pair of stepped proximal sidewalls11P over each inter-gate region of the shallow trench isolationstructure 20 is the same as the gate length GL, as illustrated in FIG.10D.

In one embodiment, each of the gate electrodes (52, 54) comprises asemiconductor gate electrode portion 52 contacting a top surface of arespective one of the gate dielectrics 50, and a metallic gate electrodeportion 54 that overlies the semiconductor gate electrode portion 52. Inone embodiment, the semiconductor gate electrode portion 52 contactssidewalls of a pair of inter-gate regions of the shallow trenchisolation structure 20. In one embodiment, the semiconductor gateelectrode portion comprises a top surface located within a samehorizontal plane as topmost surface segments of the a pair of inter-gateregions of the shallow trench isolation structure 20. In one embodiment,the metallic gate electrode portion 54 contacts the topmost surfacesegments of the pair of inter-gate regions of the shallow trenchisolation structure 20.

In one embodiment shown in FIG. 10B, lengthwise sidewalls of themetallic gate electrode portion 54 that are perpendicular to the firsthorizontal direction hd1 are vertically coincident with lengthwisesidewalls of the semiconductor gate electrode portion 52 within eachgate electrode (52, 54). However, as shown in FIG. 10C, widthwisesidewalls of the metallic gate electrode portion 54 that are parallel tothe first horizontal direction hd1 are laterally offset outward fromwidthwise sidewalls of the semiconductor gate electrode portion 52within each gate electrode (52, 54).

Referring to FIGS. 11A-11D, the patterned photoresist layer 47 can beremoved, for example, by ashing. A dielectric gate spacer material layercan be conformally deposited, and an anisotropic etch process can beperformed to remove horizontally-extending portions of the dielectricgate spacer material layer. The dielectric gate spacer material layerincludes a dielectric material such as silicon oxide and/or siliconnitride, and may be formed by at least one chemical vapor depositionprocess such as at least one low pressure chemical vapor deposition(LPCVD) process. Remaining portion of the dielectric gate spacermaterial layer comprise dielectric gate spacers 56 that laterallysurround a respective one of the gate stacks (50, 52, 54, 58). In anillustrative example, each dielectric gate spacer 56 can have a width,as measured along the first horizontal direction hd1 over a transistoractive region 10A between an inner sidewall and an outer sidewall, in arange from 5 nm to 100 nm, such as from 10 nm to 50 nm, although lesserand greater widths may also be employed.

According to an aspect of the present disclosure, the thickness of thedielectric gate spacer material layer can be greater than one half ofthe spacing between neighboring pairs of gate stacks (50, 52, 54, 58)that are laterally spaced apart along the second horizontal directionhd2. For example, the thickness of the dielectric gate spacer materiallayer can be greater than one half of the width of each opening 47A inthe patterned photoresist layer 47 along the second horizontal directionhd2 as employed at the processing steps of FIGS. 9A-9D and 10A-10D. Inthis case, vertical growth surfaces of the dielectric gate spacermaterial layer merge to form a seam between each neighboring pair ofgate stacks (50, 52, 54, 58) that are laterally spaced apart along thesecond horizontal direction hd2. After the anisotropic etch process thatforms the dielectric gate spacers 56, neighboring pairs of dielectricgate spacers 56 arranged along the second horizontal direction hd2contact each other at a vertical plane located midway between theneighboring pairs of dielectric gate spacers 56 and extending along thefirst horizontal direction hd2. All inter-gate regions of the shallowtrench isolation structure 20 can be covered by the dielectric gatespacers 56.

Generally, each neighboring pair of dielectric gate spacers 56 that arelaterally spaced along the second horizontal direction hd1 can contacteach other along a respective vertical plane that is parallel to thefirst horizontal direction hd1. In one embodiment, outer widthwisesidewalls of a neighboring pair of dielectric gate spacers 56 contacteach other at a vertical seam that laterally extends along the firsthorizontal direction hd1 above each inter-gate region of the shallowtrench isolation structure 20.

Each of the via cavities 11 can be filled by downward-protrudingportions of a respective pair of dielectric gate spacers 56. Eachneighboring pair of the dielectric gate spacers 56 that are arrangedalong the second horizontal direction hd2 can be in contact with eachother over a respective inter-gate region of the shallow trenchisolation structure 20, which comprises a pair of via cavities 11 filledwith downward-protruding portions of a respective neighboring pair ofthe dielectric gate spacers 56.

In one embodiment, each of the dielectric gate spacers 56 comprises apair of inner lengthwise sidewalls that face toward a respective gateelectrode (52, 54), laterally extend along a second horizontal directionhd2, and laterally spaced apart along the first horizontal direction hd1by the first spacing S1, i.e., by the gate spacer 55 inner sidewallspacing. In one embodiment, each of the dielectric gate spacers 56comprises a pair of outer lengthwise sidewalls that face away from therespective gate electrode (52, 54), laterally extend along the secondhorizontal direction hd2, and laterally spaced apart along the firsthorizontal direction by a third spacing S3, which is herein referred toas a gate spacer outer sidewall spacing. In one embodiment, the thirdspacing S3 (i.e., the gate spacer outer sidewall spacing) can be greaterthan the second spacing S2 (i.e., the trench distal sidewall spacing).

In one embodiment, each inter-gate region of the shallow trenchisolation structure comprises a pair of sidewall segments that laterallyextend along the first horizontal direction hd1, adjoined to arespective topmost surface segment of the inter-gate region of theshallow trench isolation structure 20, and contacted by a sidewall of arespective one of the dielectric gate spacers 56. In one embodiment, thedielectric gate spacer 56 can comprise four downward-protruding portionsvertically extending into four via cavities 11 within the shallow trenchisolation structure 20. In one embodiment, the shallow trench isolationstructure 20 can have a planar top surface located in a horizontal planeand within areas that are not covered by the gate electrodes (52, 54) orby the dielectric gate spacers 56.

Thus, the dielectric offset spacers 55 are formed only on two sides ofeach of the gate electrodes (52, 54) which extend in the secondhorizontal direction hd2 and are absent on the other two sides of eachof the gate electrodes (52, 54) which extend in the perpendicular firsthorizontal direction hd1. In contrast, gate dielectric spacers 56laterally surround each of the gate electrodes (52, 54) on all foursides. Thus, the gate dielectric spacers 56 physically contact thedielectric offset spacers 55 located on two sides of each of the gateelectrodes (52, 54) which extend in the second horizontal direction hd2,and the gate dielectric spacers 56 physically contact the other twosides of each of the gate electrodes (52, 54) which extend in the firsthorizontal direction hd1.

Referring to FIGS. 12A-12D, additional electrical dopants of the secondconductivity type can be implanted into unmasked portions of thesemiconductor material layer 10 that are not masked by the gate stacks(50, 52, 54, 58), and the dielectric gate spacers 56 to form deepsource/drain regions (32, 38).

According to an aspect of the present disclosure, the gaps betweenneighboring pairs of gate electrodes (52, 54) that are laterally spacedapart along the second horizontal direction hd2 are filled with a pairof dielectric gate spacers 56. Thus, the additional electrical dopantsof the second conductivity type are not implanted into portions of thetransistor active regions 10A that are proximal to the widthwise edgesof the metallic gate electrode portions 54 and the gate cap dielectrics58 that are parallel to the first horizontal direction hd1. Thischaracteristic enables reduction of the lateral spacing betweenneighboring pairs of semiconductor active regions 10A without concernfor collateral implantation of dopants of the second conductivity typeinto peripheral portions of the semiconductor active regions 10A thatare proximal to the widthwise edges of the metallic gate electrodeportions 54 and the gate cap dielectrics 58 that are parallel to thefirst horizontal direction hd1.

The deep source/drain regions (32, 38) may include, for example, deepsource regions 32 and deep drain regions 38. Generally, the atomicconcentration of dopants in the deep source/drain region (32, 38) isgreater than the atomic concentration of dopants in the source/drainextension regions (31, 39). As such, volumes of the source/drainextension regions (31, 39) that overlap with volumes of the deepsource/drain region (32, 38) are incorporated into a respective one ofthe deep source/drain region (32, 38). In one embodiment, the atomicconcentration of dopants in the deep source/drain regions (32, 38) maybe in a range from 5.0×10¹⁸/cm³ to 2.0×10²¹/cm³, although lesser andgreater dopant concentrations may also be employed.

Unimplanted portions of each transistor active region 10A constitutes achannel region 36. Each channel region 36 may have an atomicconcentration of dopants of the first conductivity type in a range from1.0×10¹⁴/cm³ to 1.0×10¹⁸/cm³, although lesser and greater dopantconcentrations may also be employed. Each contiguous combination of arespective one of source/drain extension regions (31, 39) and arespective one of the deep source/drain region (32, 38) constitutes asource/drain region, which may be a source region (31, 32) including acombination of a source extension region 31 and a deep source region 32,or may be drain region (38, 39) including a combination of a drainextension region 39 and a deep drain region 38. Generally, a sourceregion (32, 32) and a drain region (38, 39) can be formed in portions ofeach transistor active region 10A that are laterally spaced from eachother by a respective channel region 36.

Referring to FIGS. 13A-13D, at least one dielectric liner (62, 64) canbe optionally formed over the physically exposed surfaces of the firstexemplary structure by at least one conformal deposition process. The atleast one dielectric liner (62, 64) may comprise, for example, a stackof a silicon oxide liner 62 and a silicon nitride liner 64. Acontact-level dielectric layer 80 can be deposited over the gate stacks(50, 52, 54, 58), the source/drain regions{(31, 32), (38, 39)}, theshallow trench isolation structure 20, and the optional at least onedielectric liner (62, 64). The contact-level dielectric layer 80comprises a dielectric material such as silicon oxide. A planarizationprocess such as a chemical mechanical planarization process can beoptionally performed to planarize the top surface of the contact-leveldielectric layer 80. The vertical distance between the top surface ofthe contact-level dielectric layer 80 and the top surfaces of the gatecap dielectrics 58 may be in a range from 50 nm to 500 nm, althoughlesser and greater vertical distances may also be employed.

Referring to FIGS. 14A-14C, contact via cavities can be formed throughthe contact-level dielectric layer 80, and can be filled with at leastone conductive material such as at least one metallic material. Excessportions of the at least one conductive material can be removed fromabove the horizontal plane including the top surface of thecontact-level dielectric layer 80 by a planarization process, which mayinclude a recess etch process and/or a chemical mechanical planarizationprocess. Each remaining portion of the at least one conductive materialconstitutes a contact via structure (82, 85, 88). The contact viastructures (82, 85, 88) may comprise source contact via structures 82contacting a respective one of the source regions (31, 32), draincontact via structures 88 contacting a respective one of the drainregions (38, 39), and gate contact via structures 85 contacting arespective one of the gate electrodes (52, 54).

Referring collectively to FIGS. 1A-14D and according to variousembodiments of the present disclosure, a semiconductor structurecomprises a first field effect transistor 100A, a second field effecttransistor 100B and a shallow trench isolation structure 20. Each of thefirst and second field effect transistors (100A, 100B) comprises asemiconductor active region 10A including a source region (31, 32), achannel region 36, and a drain region (38, 39) arranged along a firsthorizontal direction hd1, a gate dielectric 50 contacting a top surfaceof the channel region 36, a gate electrode (52, 54) overlying the gatedielectric 50, and a dielectric gate spacer 56 laterally surrounding thegate electrode (52, 54). The shallow trench isolation 20 structurelaterally surrounds each of the semiconductor active regions 10A of thefirst and second two field effect transistors (100A, 100B). The shallowtrench isolation structure 20 has a planar top surface between two viacavities 11 extending in the first horizontal direction hd1 and locatedin an inter-gate region between the gate electrodes (52, 54) of thefirst and second field effect transistors (100A, 100B), and thedielectric gate spacers 56 of the first and the second field effecttransistors (100A, 100B) contain downward-protruding portions which fillthe two via cavities 11 in the shallow trench isolation structure 20.

In one embodiment, dielectric offset spacers 55 are located only on twosides of each of the gate electrodes (52, 54) which extend in a secondhorizontal direction hd2 which is perpendicular to the first horizontaldirection hd1. The gate dielectric spacers 56 laterally surround each ofthe gate electrodes (52, 54) on all four sides. The gate dielectricspacers 56 physically contact the dielectric offset spacers 55 over thetwo sides of each of the gate electrodes (52, 54) which extend in thesecond horizontal direction h2, and the gate dielectric spacers 56physically contact another two sides of each of the gate electrodes (52,54) which extend in the first horizontal direction hd1.

In one embodiment, each of the dielectric gate spacers 56 comprises apair of inner lengthwise sidewalls that face toward a respective gateelectrode (52, 54), laterally extend along the second horizontaldirection hd2, and laterally spaced apart along the first horizontaldirection hd1 by a gate spacer inner sidewall spacing (such as the firstspacing S1); and the pair of via cavities 11 comprises a pair ofproximal sidewalls 11P that are laterally spaced apart along the firsthorizontal direction hd1 by the gate spacer inner sidewall spacing

In one embodiment, each of the dielectric gate spacers 56 comprises apair of outer lengthwise sidewalls that face away from the respectivegate electrode (52, 54), laterally extend along the second horizontaldirection hd2, and laterally spaced apart along the first horizontaldirection hd1 by a gate spacer outer sidewall spacing (such as the thirdspacing S3); and the pair of via cavities 11 comprises a pair of distalsidewalls 11D that are laterally spaced apart along the first horizontaldirection hd1 by a trench distal sidewall spacing (such as the secondspacing S2) that is less than the gate spacer outer sidewall spacing(such as the third spacing S3).

In one embodiment, outer widthwise sidewalls of a neighboring pair ofdielectric gate spacers 56 contact each other at a vertical seam thatlaterally extends along the first horizontal direction hd1 above eachinter-gate region of the shallow trench isolation structure 20.

In one embodiment, each inter-gate region of the shallow trenchisolation structure 20 comprises: a pair of topmost horizontal surfacesegments THSS contacting a respective bottom surface segment of aneighboring pair of gate electrodes (52, 54); and an intermediatehorizontal surface segment IHSS that is adjoined to the topmosthorizontal surface segments THSS by a pair of vertical surface segmentsand located between a respective pair of via cavities 11. In oneembodiment, the intermediate horizontal surface segment IHSS is locatedabove the planar top surface of the shallow trench isolation structure20.

In one embodiment, bottom surfaces of the via cavities 11 are locatedbelow the planar top surface of the shallow trench isolation structure20. In one embodiment, each of the via cavities 11 comprises a pair ofstepped proximal sidewalls having a respective horizontal step locatedbetween an upper vertical proximal sidewall segment and a lower verticalproximal sidewall segment; each of the gate electrodes (52, 54)comprises a pair of lengthwise sidewalls that are laterally spaced apartalong the first horizontal direction hd1 by a gate length GL; and alateral spacing between a pair of horizontal steps of the pair ofstepped proximal sidewalls over each inter-gate region of the shallowtrench isolation structure 20 is the same as the gate length GL.

In one embodiment, each of the gate electrodes (52, 54) comprises: asemiconductor gate electrode portion 52 contacting a top surface of arespective one of the gate dielectrics 50; and a metallic gate electrodeportion 54 that overlies the semiconductor gate electrode portion 52. Inone embodiment, the semiconductor gate electrode portion 52 contactssidewalls of a pair of inter-gate regions of the shallow trenchisolation structure 20; the semiconductor gate electrode portion 52comprises a top surface located within a same horizontal plane astopmost surface segments of the a pair of inter-gate regions of theshallow trench isolation structure 20; and the metallic gate electrodeportion 54 contacts the topmost surface segments of the pair ofinter-gate regions of the shallow trench isolation structure 20.

In one embodiment, lengthwise sidewalls of the metallic gate electrodeportion 54 that are perpendicular to the first horizontal direction hd1are vertically coincident with lengthwise sidewalls of the semiconductorgate electrode portion 52; widthwise sidewalls of the metallic gateelectrode portion 54 that are parallel to the first horizontal directionhd1 are laterally offset outward from widthwise sidewalls of thesemiconductor gate electrode portion 52; and each inter-gate region ofthe shallow trench isolation structure 20 comprises a pair of sidewallsegments that laterally extend along the first horizontal direction hd1,adjoined to a respective topmost surface segment of the inter-gateregion of the shallow trench isolation structure 20, and contacted by asidewall of a respective one of the dielectric gate spacers 56.

In one embodiment, each dielectric gate spacer 56 within the first andsecond field effect transistors (100A, 100B) comprises fourdownward-protruding portions vertically extending into four via cavities11 within the shallow trench isolation structure 20.

In one embodiment, each of the via cavities 11 comprises: a pair offirst sidewalls 111 that are parallel to the first horizontal directionhd1 and vertically coincident with widthwise sidewalls of a neighboringpair of gate electrodes (52, 54); and a pair of second sidewalls (suchas a proximal sidewall 11P and a distal sidewall 11D) that areperpendicular to the first horizontal direction hd1 and adjoined tovertically-extending edges of the pair of first sidewalls 111. In oneembodiment, each of the gate electrodes (52, 54) comprises a pair oflengthwise sidewalls that is perpendicular to the first horizontaldirection hd1 and laterally spaced apart along the first horizontaldirection hd1 by a gate length GL; and the pair of second sidewallscomprises a pair of sidewall segments (such as upper sidewall segmentsof proximal sidewalls 11P) that are laterally spaced apart along thefirst horizontal direction hd1 by the gate length GL.

In another embodiment, a field effect transistor 100A comprises asemiconductor active region 10A including a source region (31, 32), achannel region 36, and a drain region (38, 39) arranged along a firsthorizontal direction hd1, a gate dielectric 50 contacting a top surfaceof the channel region 36, a gate electrode (52, 54) having four sidesoverlying the gate dielectric 50, a dielectric gate spacer 56 laterallysurrounding the gate electrode (52, 54) on the four sides, anddielectric offset spacers 55 located only on two sides of the gateelectrode (52, 54) which extend in a second horizontal direction hd2which is perpendicular to the first horizontal direction hd1. The gatedielectric spacers 56 physically contact the dielectric offset spacers55 over the two sides of the gate electrode (52, 54) which extend in thesecond horizontal direction hd2, and the gate dielectric spacers 56physically contact another two sides of the gate electrode (52, 54)which extend in the first horizontal direction hd1.

In the above described first embodiment of the present disclosure, thegate strip is divided into the gate stacks before forming the dielectricgate spacer 56 and the deep source/drain regions (32, 38). However, in asecond embodiment of the present disclosure, the gate strip is dividedinto the gate stacks after forming the dielectric gate spacer 56 and thedeep source/drain regions (32, 38).

Referring to FIGS. 15A-15D, a second exemplary structure according tothe second embodiment of the present disclosure can be derived from thefirst exemplary structure of FIGS. 8A-8D by forming a dielectric gatespacer 56 around each gate strip (50, 52, 54S, 58S) after performing theLDD ion implantation step shown in FIGS. 8A-8D. A dielectric gate spacermaterial layer can be conformally deposited on the dielectric offsetspacers 55 located on the sidewalls of the gate strip, and ananisotropic etch process can be performed to removehorizontally-extending portions of the dielectric gate spacer materiallayer. The dielectric gate spacer material layer includes a dielectricmaterial such as silicon oxide and/or silicon nitride, and may be formedby at least one chemical vapor deposition process such as at least onelow pressure chemical vapor deposition (LPCVD) process. Remainingportion of the dielectric gate spacer material layer comprise dielectricgate spacers 56 that laterally surround a respective gate strip (50, 52,54S, 58S). In an illustrative example, each dielectric gate spacer 56can have a width, as measured along the first horizontal direction hd1over a transistor active region 10A between an inner sidewall and anouter sidewall, in a range from 5 nm to 100 nm, such as from 10 nm to 50nm, although lesser and greater widths may also be employed.

Generally, each gate strip (50, 52, 54S, 58S) can extend along thesecond horizontal direction hd2 over a plurality of semiconductor activeregions (i.e., the transistor active regions 10A), and can comprise aplurality of gate dielectrics 50 and a gate electrode strip (52, 54S).The gate electrode strip (52, 54S) can comprise a plurality ofsemiconductor gate electrode portions 52 and a metallic gate electrodestrip 54S. Each dielectric gate spacer 56 laterally surrounds arespective gate strip (50, 52, 54S, 58S), and laterally extends alongthe second horizontal direction hd2 over a plurality of semiconductoractive regions 10A. Each dielectric gate spacer 56 can be formed over,and directly on, a plurality of source extension regions 31 that arearranged along the second horizontal direction hd2 and over, anddirectly on, a plurality of drain extension regions 39 that are arrangedalong the second horizontal direction hd2.

Referring to FIGS. 16A-16D, additional electrical dopants of the secondconductivity type can be implanted into unmasked portions of thesemiconductor material layer 10 that are not masked by a combination ofthe gate strips (50, 52, 54S, 58S) and the dielectric gate spacers 56 toform deep source/drain regions (32, 38). The deep source/drain regions(32, 38) may include, for example, deep source regions 32 and deep drainregions 38. Generally, the atomic concentration of dopants in the deepsource/drain region (32, 38) is greater than the atomic concentration ofdopants in the source/drain extension regions (31, 39). As such, volumesof the source/drain extension regions (31, 39) that overlap with volumesof the deep source/drain region (32, 38) are incorporated into arespective one of the deep source/drain region (32, 38). In oneembodiment, the atomic concentration of dopants in the deep source/drainregions (32, 38) may be in a range from 5.0×10¹⁸/cm³ to 2.0×10²¹/cm³,although lesser and greater dopant concentrations may also be employed.

According to an aspect of the present disclosure, the gate strips (50,52, 54S, 58S) cover the entire inter-gate region of the shallow trenchisolation structure 20 located between a neighboring pair of transistoractive regions 10A. Thus, the additional electrical dopants of thesecond conductivity type are not implanted into portions of thetransistor active regions 10A that are proximal to the widthwise edgesof gate electrodes to be subsequently patterned from the gate strips(50, 52, 54S, 58S). Thus, the lateral spacing between neighboring pairsof semiconductor active regions 10A may be reduced without collateralimplantation of dopants of the second conductivity type into peripheralportions of the semiconductor active regions 10A that are proximal tothe widthwise edges of the gate electrodes (i.e., in the gate fringeregion) to be subsequently patterned from the gate strips (50, 52, 54S,58S).

Unimplanted portions of each transistor active region 10A constitutes achannel region 36. Each channel region 36 may be in a range from1.0×10¹⁴/cm³ to 1.0×10¹⁸/cm³, although lesser and greater dopantconcentrations may also be employed. Each contiguous combination of arespective one of source/drain extension regions (31, 39) and arespective one of the deep source/drain region (32, 38) constitutes asource/drain region, which may be a source region (31, 32) including acombination of a source extension region 31 and a deep source region 32,or may be drain region (38, 39) including a combination of a drainextension region 39 and a deep drain region 38. Generally, a sourceregion (32, 32) and a drain region (38, 39) can be formed in portions ofeach transistor active region 10A that are laterally spaced from eachother by a respective channel region 36 in a plan view.

Referring to FIGS. 17A-17D, a photoresist layer 47 can be applied overthe gate strips (50, 52, 54S, 58S), the dielectric gate spacers 56, andthe plurality of semiconductor active regions (i.e., the transistoractive regions 10A). The photoresist layer 47 can be lithographicallypatterned to form openings 47A that straddle portions of the gate strips(50, 52, 54S, 58S) that overlie top surfaces of the shallow trenchisolation structure 20. The patterned photoresist layer 47 comprises atleast one row of openings (which may comprise a plurality of rows ofopenings) 47A arranged along the second horizontal direction hd2 andlocated within the areas of the shallow trench isolation structure 20.In one embodiment, each opening 47A in the patterned photoresist layer47 comprises a pair of first edges that straddle a respective underlyinggate strip (50, 52, 54S, 58S) and a pair of second edges that overlie arespective dielectric gate spacer 56.

Generally, the patterned photoresist layer 47 can cover the entire areaof each of the transistor active regions 10A that is not covered by thegate strips (50, 52, 54S, 58S) or the dielectric gate spacers 56. Thepatterned photoresist layer 47 includes rectangular openings 47A inareas in which the gate strips (50, 52, 54S, 58S) are subsequently cut.In other words, the areas of the openings 47A in the patternedphotoresist layer 47 correspond to areas from which portions of the gatestrips (50, 52, 54S, 58S) are subsequently removed. In one embodiment,the patterned photoresist layer 47 comprises a row of openings 47Aarranged along the second horizontal direction hd1 and located withinthe areas of the shallow trench isolation structure 20 and having anareal overlap with a respective portion of an underlying gate strip (50,52, 54S, 58S). In one embodiment, a row of rectangular openings 47A canbe formed in the patterned photoresist layer 47 over each gate strip(50, 52, 54S, 58S).

In one embodiment, each of the rectangular openings 47A in the patternedphotoresist layer 47 can have a pair of first straight sidewalls and apair of second straight sidewalls. The pair of first straight sidewallscan laterally extend along the first horizontal direction hd1 and havinga greater length than the gate length GL (i.e., the lateral dimensionalong the first horizontal direction hd1) of the underlying gate strip(50, 52, 54S, 58S). In one embodiment, the pair of first straightsidewalls can overlie a respective one of the transistor active regions10A, i.e., can have an areal overlap with the respective one of thetransistor active regions 10A in a plan view along a vertical directionthat is perpendicular to the top surface of the semiconductor substrate8. The pair of second sidewalls can laterally extend along the secondhorizontal direction hd2, overlie and contact a top surface of arespective dielectric gate spacer 56, and does not have an areal overlapwith the underlying gate strip (50, 52, 54S, 58S). The pair of secondsidewalls of each opening 47A in the patterned photoresist layer 47 mayhave an areal overlap with peripheral regions of a neighboring pair oftransistor active regions 10A.

A top surface segment of a gate cap dielectric 58 and two segments ofouter sidewalls of a dielectric gate spacer 56 can be physically exposedwithin the area of each opening 47A in the patterned photoresist layer47. The width of each rectangular opening in the patterned photoresistlayer 47 along the second horizontal direction hd2 can be greater thanthe lateral spacing between a neighboring pair of transistor activeregions 10A along the second horizontal direction hd2, and can be lessthan the lateral spacing between a neighboring pair of gate dielectrics50 that are laterally spaced along the second horizontal direction hd2.The openings 47A in the patterned photoresist layer 47 do not have anyareal overlap with the gate dielectrics 50. The length of eachrectangular opening 47A in the patterned photoresist layer 47 along thefirst horizontal direction hd1 can be greater than the gate length of anunderlying gate strip (50, 52, 54S, 58S), which is the width of theunderlying gate strip (50, 52, 54S, 58S) along the first horizontaldirection hd1.

Referring to FIGS. 18A-18D, an anisotropic etch process can be performedto etch unmasked portions of the gate strips (50, 52, 54S, 58S) and thedielectric gate spacers 56. The pattern of rows of openings 47A in thepatterned photoresist layer 47 can be transferred through the gatestrips (50, 52, 54S, 58S) and into unmasked areas of the dielectric gatespacers 56. Unmasked portions of the offset spacers 55 can becollaterally vertically recessed during the anisotropic etch process.The shallow trench isolation structure 20 is masked by the patternedphotoresist layer 47, and is not etched during the anisotropic etchprocess.

The pattern of the rows of openings in the patterned photoresist layer47 can be transferred through the gate strips (50, 52, 54S, 58S) andinto unmasked portions of the dielectric gate spacers 56 by theanisotropic etch process. Unmasked portions of the gate strips (50, 52,54S, 58S) are removed by the anisotropic etch process, and remainingportions of the gate strips (50, 52, 54S, 58S) comprise a plurality ofgate stacks (50, 52, 54, 58).

Each gate strip (50, 52, 54S, 58S) can be divided into the gate stacks(50, 52, 54, 58) by removing unmasked portions of the respective gatestrip (50, 52, 54S, 58S). Each gate electrode strip (52, 54S) can bedivided into a respective plurality of gate electrodes (52, 54) that arelaterally spaced apart along the second horizontal direction hd2 andoverlies a respective one of the plurality of semiconductor activeregions 10A. Each gate stack (50, 52, 54, 58) includes a vertical stackof a gate dielectric 50, a semiconductor gate electrode portion 52, ametallic gate electrode portion 54, and a gate cap dielectric 58. Eachmetallic gate electrode portion 54 is a patterned portion of arespective metallic gate electrode strip 54S. Each gate cap dielectric58 is a patterned portion of a gate cap dielectric strip 58S. Each ofthe gate dielectrics 50 is one of a plurality of gate dielectrics 50within a respective one of the gate strips (50, 52, 54S, 58S). Eachcontiguous combination of a semiconductor gate electrode portion 52 anda metallic gate electrode portion 54 constitutes a gate electrode (52,54). Thus, each of the gate electrodes (52, 54) is a patterned portionof a respective gate electrode strip (52, 54S).

Each gate stack (50, 52, 54, 58) is formed over a respective one of thetransistor active regions 10A. Each gate stack comprises a gatedielectric 50 and a gate electrode (52, 54).

In one embodiment, the anisotropic etch process etches the materials ofthe gate strips (50, 52, 54S, 58S) at a higher etch rate than thematerial of the dielectric gate spacers 56. A pair of stepped sidewallscan be formed on each dielectric gate spacer 56 underneath each openingin the patterned photoresist layer 47.

In one embodiment, each dielectric gate spacer 56 comprisesover-active-region gate spacer portions 56A overlying the semiconductoractive regions 10A, as shown in FIG. 18C. The over-active-region gatespacer portions 56A comprises straight inner sidewalls that areperpendicular to the first horizontal direction hd1 and laterally spacedapart by a first spacing S1, which is also referred to as a gate spacerinner sidewall spacing, i.e., the spacing between a pair of innersidewalls of a dielectric gate spacer 56. In one embodiment, eachdielectric gate spacer 56 also comprises inter-active-region gate spacerportions 56B overlying portions of the shallow trench isolationstructure 20, as shown in FIG. 18D. The inter-active-region gate spacerportion 56B comprises stepped sidewalls including a lower straightsidewall segment 56L adjoined to, and located within same verticalplanes as, a respective pair of straight inner sidewalls of neighboringover-active-region gate spacer portions 56A, an upper straight sidewallsegment 56U that is laterally offset from the lower straight sidewallsegment, and a connecting horizontal surface 56H that is adjoined to atop edge of the lower straight sidewall segment and to a bottom edge ofthe upper straight sidewall segment. A pair of upper straight sidewallsegments 56U of two inter-active-region gate spacer portions 56B locatedwithin a same opening 47A in the patterned photoresist layer 47 can belaterally spaced apart from each other by a second spacing S2′, which isherein referred to as a gate spacer upper inner sidewall segmentspacing. A lateral distance between outer sidewalls of each dielectricgate spacer 56 along the first horizontal direction hd1 can be uniform,and is herein referred to as a third spacing S3, which is also referredto as a gate spacer outer sidewall spacing. The second spacing S2′ canbe less than the third spacing S3.

In one embodiment, the shallow trench isolation structure 20 can have aplanar top surface located in a horizontal plane and at least withinareas that are covered by the patterned photoresist layer 47 or by thedielectric gate spacers 56. The lower straight sidewall segments 56L ofthe inter-active-region gate spacer portions 56B can contact the planartop surface of the shallow trench isolation structure 20. In oneembodiment, each of the upper straight sidewall segments 56U of theinter-active-region gate spacer portions 56B has a respective top edgethat that is adjoined to a top edge of a respective segment of a concaveouter sidewall of the inter-active-region gate spacer portions 56B ofthe dielectric gate spacers 56.

In one embodiment, the shallow trench isolation structure 20 comprisesinter-gate regions located between a neighboring pair of semiconductoractive regions 10A and within an area enclosed by an outer periphery ofa respective dielectric gate spacer 56. A pair of theinter-active-region gate spacer portions 56B overlies each of theinter-gate regions. In one embodiment, upper straight sidewall segments56U of the pair of inter-active-region gate spacer portions 56B arelaterally spaced from each other along the first horizontal directionhd1 by a gate spacer upper inner sidewall segment spacing (such as thesecond spacing S2′). Lower straight sidewall segments 56L of the pair ofinter-active-region gate spacer portions 56B are laterally spaced apartfrom each other along the first horizontal direction by a gate spacerinner sidewall spacing (such as the first spacing S1) that is less thanthe gate spacer upper inner sidewall segment spacing. In embodiments inwhich the offset spacers 55 are omitted, the gate spacer inner sidewallspacing (such as the first spacing S1) may be the same as the gatelength. In one embodiment, a pair of straight inner sidewalls of each ofthe over-active-region gate spacer portions 56A can be laterally spacedapart along the first horizontal direction by the gate spacer innersidewall spacing (such as the first spacing S1).

Referring to FIGS. 19A-19E, the patterned photoresist layer 47 can beremoved, for example, by ashing. In one embodiment, the straight innersidewalls of the over-active-region gate spacer portions 56A verticallyextend at least from a first horizontal plane HP1 including bottomsurfaces of the gate electrodes (52, 54) and at least to a secondhorizontal plane HP2 including top surfaces of the gate electrodes (52,54). The entirety of the connecting surfaces of the over-active-regiongate spacer portions 56A is located above the first horizontal plane HP1and below the second horizontal plane HP2. In one embodiment, thestraight inner sidewalls of the over-active-region gate spacer portions56A contact top surfaces of the source regions (31, 32) and the drainregions (38, 39).

Referring to FIGS. 20A-20D, at least one dielectric material layer (62,64, 80) can be deposited over the second exemplary structure. In oneembodiment, the at least one dielectric material layer (62, 64, 80)comprises a vertical stack comprising at least one conformal dielectricliner (62, 64) and a contact-level dielectric layer 80 overlying the atleast one conformal dielectric liner (62, 64). Each of the at least onedielectric liner (62, 64) can be deposited over the physically exposedsurfaces of the gate stacks (50, 52, 54, 58), the dielectric gatespacers 56, the source regions (31, 32), and the drain regions (38, 39)by at least one conformal deposition process. The at least onedielectric liner (62, 64) may comprise, for example, a stack of asilicon oxide liner 62 and a silicon nitride liner 64. A contact-leveldielectric layer 80 can be deposited over the gate stacks (50, 52, 54,58), the source/drain regions{(31, 32), (38, 39)}, the shallow trenchisolation structure 20, and the optional at least one dielectric liner(62, 64). The contact-level dielectric layer 80 comprises a dielectricmaterial, such as silicon oxide. A planarization process such as achemical mechanical planarization process can be optionally performed toplanarize the top surface of the contact-level dielectric layer 80. Thevertical distance between the top surface of the contact-leveldielectric layer 80 and the top surfaces of the gate cap dielectrics 58may be in a range from 50 nm to 500 nm, although lesser and greatervertical distances may also be employed. The contact via structures (82,85, 88) are then formed through the contact-level dielectric layer 80 asdescribed above.

Referring collectively to FIGS. 1A-8D and 15A-20D and according to thesecond embodiment of the present disclosure, a semiconductor structurecomprises a first field effect transistor 200A and a second field effecttransistor 200B and a shallow trench isolation structure 20. Each of thefirst and second field effect transistors (200A, 200B) comprises asemiconductor active region 10A including a source region (31, 32), achannel region 36, and a drain region (38, 39) arranged along a firsthorizontal direction hd1, a gate dielectric 50 contacting a top surfaceof the channel region 36, a gate electrode (52, 54) overlying the gatedielectric 50, and a pair of dielectric gate spacers 56 located onopposite sides of the gate electrode (52, 54). The shallow trenchisolation 20 structure laterally surrounds each of the semiconductoractive regions 10A of the first and second two field effect transistors(200A, 200B). Each of the pair of dielectric gate spacers 56 comprisesover-active-region gate spacer portions 56A overlying the semiconductoractive regions 10A and comprising straight inner sidewalls that areperpendicular to the first horizontal direction hd1, andinter-active-region gate spacer portions 56B overlying portions of theshallow trench isolation structure 20 and comprising stepped sidewallsincluding a lower straight sidewall segment 56L adjoined to a respectivepair of straight inner sidewalls, an upper straight sidewall segment 56Uthat is laterally offset from the lower straight sidewall segment 56L,and a connecting surface 56H that is adjoined to a top edge of the lowerstraight sidewall segment and to a bottom edge of the upper straightsidewall segment.

In one embodiment, the straight inner sidewalls vertically extend atleast from a first horizontal plane HP1 including bottom surfaces of thegate electrodes (52, 54) and at least to a second horizontal plane HP2including top surfaces of the gate electrodes (52, 54). In oneembodiment, the entirety of the connecting surface 56H is located abovethe first horizontal plane HP1 and below the second horizontal planeHP2. In one embodiment, the straight inner sidewalls contact topsurfaces of the source regions (31, 32) and the drain regions (38, 39).

In one embodiment, the shallow trench isolation structure 20 has aplanar top surface located in a horizontal plane and within areas thatare not covered by the gate electrodes (52, 54); and the lower straightsidewall segments 56L contact the planar top surface of the shallowtrench isolation structure 20.

In one embodiment, each of the straight inner sidewalls has a respectivetop edge that is adjoined to a top edge of a respective segment of aconcave outer sidewall of the dielectric gate spacer 56; and each of theupper straight sidewall segments 56U has a respective top edge that thatis adjoined to a top edge of a respective additional segment of theconcave outer sidewall of the dielectric gate spacer 56.

In one embodiment, the shallow trench isolation structure 20 comprisesinter-gate regions located between a neighboring pair of semiconductoractive regions 10A and within an area enclosed by an outer periphery ofthe dielectric gate spacer 56; and a pair of inter-active-region gatespacer portions 56B overlies each of the inter-gate regions.

In one embodiment, upper straight sidewall segments 56U of the pair ofinter-active-region gate spacer portions 56B are laterally spaced fromeach other along the first horizontal direction hd1 by a gate spacerupper inner sidewall segment spacing (such as a second spacing S2′); andlower straight sidewall segments 56L of the pair of inter-active-regiongate spacer portions 56B are laterally spaced apart from each otheralong the first horizontal direction hd1 by a gate spacer inner sidewallspacing (such as a first spacing S1) that is less than the gate spacerupper inner sidewall segment spacing. In one embodiment, a pair ofstraight inner sidewalls of each of the over-active-region gate spacerportions 56A is laterally spaced apart along the first horizontaldirection hd1 by the gate spacer inner sidewall spacing.

In one embodiment, the semiconductor structure comprises at least onedielectric material layer (62, 64, 80) overlying the gate electrodes(52, 54) and the dielectric gate spacer 56, wherein each of the gateelectrodes (52, 54) comprises a respective widthwise sidewall that isparallel to the first horizontal direction hd1 and in direct contactwith the at least one dielectric material layer (62, 64, 80) (such asthe silicon oxide liner 62). In one embodiment, at least one of the gateelectrodes (52, 54) comprises a pair of widthwise sidewalls that contacta respective sidewall of the at least one dielectric material layer (62,64, 80) (such as the silicon oxide liner 62).

In one embodiment, the at least one dielectric material layer (62, 64,80) comprises a vertical stack comprising at least one conformaldielectric liner (62, 64) and a contact-level dielectric layer 80overlying the at least one conformal dielectric liner (62, 64); and theat least one conformal dielectric liner (62, 64) contacts top surfacesof the source regions (31, 32), the drain regions (38, 39), the shallowtrench isolation structure 20, and each of the stepped sidewall of theinter-active-region gate spacer portions 56B. In one embodiment, the atleast one conformal dielectric liner (62, 64) contacts an entirety of anconcave outer sidewall of the dielectric gate spacer 56 that is adjoinedto top edges of the straight inner sidewalls of the over-active-regiongate spacer portions 56A and to top edges of the stepped sidewalls ofthe inter-active-region gate spacer portions 56B.

In one embodiment, each of the gate electrodes (52, 54) comprises asemiconductor gate electrode portion 52 contacting a top surface of arespective one of the gate dielectrics; and a metallic gate electrodeportion 54 that overlies the semiconductor gate electrode portion 52 andhaving a first length along a second horizontal direction hd2 that isperpendicular to the first horizontal direction hd1. The semiconductorgate electrode portion 52 comprises an upper region having the firstlength and a lower region having a second length along the secondhorizontal direction hd2 that that is greater than the first length. Thefirst length of the metallic gate electrode portion along the secondhorizontal direction hd2 is smaller than a length of the active region10A in the second horizontal direction hd2, such that an edge of themetallic gate electrode portion 54 which extends along the firsthorizontal direction hd1 is located over the active region 10A.

In one embodiment, the semiconductor gate electrode portion 52comprises: upper widthwise sidewalls that laterally extend along thefirst horizontal direction hd1 and vertically coincident with widthwisesidewalls of the metallic gate electrode portion 54; lower widthwisesidewalls that laterally extend along the second horizontal directionhd2 and contacting sidewall segments of the shallow trench isolationstructure 20; and horizontal surface segments connecting an upper edgeof a respective one of the lower widthwise sidewalls to a lower edge ofa respective one of the upper widthwise sidewalls.

The various embodiments of the present disclosure can be employed toscale a row of field effect transistors, such as a two-dimensional arrayof field effect transistors, along the lengthwise direction of gateelectrodes (52, 54), i.e., along the direction that is perpendicular tothe direction of current flow in the channel region between the sourceand drain regions within each of the field effect transistors.Specifically, at least the LDD ion implantation process can be performedprior to dividing gate strips (50, 52, 54S, 58S) into gate electrodes,thereby preventing collateral implantation of electrical dopants inproximity to widthwise edges of gate electrodes (52, 54) to besubsequently patterned. This reduces or eliminates leakage current pathsin the gate fringe area.

Although the foregoing refers to particular preferred embodiments, itwill be understood that the disclosure is not so limited. It will occurto those of ordinary skill in the art that various modifications may bemade to the disclosed embodiments and that such modifications areintended to be within the scope of the disclosure. Where an embodimentemploying a particular structure and/or configuration is illustrated inthe present disclosure, it is understood that the present disclosure maybe practiced with any other compatible structures and/or configurationsthat are functionally equivalent provided that such substitutions arenot explicitly forbidden or otherwise known to be impossible to one ofordinary skill in the art. All of the publications, patent applicationsand patents cited herein are incorporated herein by reference in theirentirety.

What is claimed is:
 1. A semiconductor structure comprising: first andsecond field effect transistors, wherein each of the first and secondfield effect transistors comprises: a semiconductor active regionincluding a source region, a channel region, and a drain region arrangedalong a first horizontal direction; a gate dielectric contacting a topsurface of the channel region; a gate electrode overlying the gatedielectric; and a dielectric gate spacer laterally surrounding the gateelectrode; and a shallow trench isolation structure which laterallysurrounds each of the semiconductor active regions of the first andsecond two field effect transistors, wherein the shallow trenchisolation structure has a planar top surface between two via cavitiesextending in the first horizontal direction and located in an inter-gateregion between the gate electrodes of the first and second field effecttransistors; and the dielectric gate spacers of the first and the secondfield effect transistors contain downward-protruding portions which fillthe two via cavities in the shallow trench isolation structure.
 2. Thesemiconductor structure of claim 1, further comprising dielectric offsetspacers located only on two sides of each of the gate electrodes whichextend in a second horizontal direction which is perpendicular to thefirst horizontal direction, wherein: the gate dielectric spacerslaterally surround each of the gate electrodes on all four sides; thegate dielectric spacers physically contact the dielectric offset spacersover the two sides of each of the gate electrodes which extend in thesecond horizontal direction; and the gate dielectric spacers physicallycontact another two sides of each of the gate electrodes which extend inthe first horizontal direction.
 3. The semiconductor structure of claim1, wherein: each of the dielectric gate spacers comprises a pair ofinner lengthwise sidewalls that face toward a respective gate electrode,laterally extend along a second horizontal direction which isperpendicular to the first horizontal direction, and laterally spacedapart along the first horizontal direction by a gate spacer innersidewall spacing; and the pair of via cavities comprises a pair ofproximal sidewalls that are laterally spaced apart along the firsthorizontal direction by the gate spacer inner sidewall spacing.
 4. Thesemiconductor structure of claim 3, wherein: each of the dielectric gatespacers comprises a pair of outer lengthwise sidewalls that face awayfrom the respective gate electrode, laterally extend along the secondhorizontal direction, and laterally spaced apart along the firsthorizontal direction by a gate spacer outer sidewall spacing; and thepair of via cavities comprises a pair of distal sidewalls that arelaterally spaced apart along the first horizontal direction by a trenchdistal sidewall spacing that is less than the gate spacer outer sidewallspacing.
 5. The semiconductor structure of claim 1, wherein outerwidthwise sidewalls of a neighboring pair of dielectric gate spacerscontact each other at a vertical seam that laterally extends along thefirst horizontal direction above each inter-gate region of the shallowtrench isolation structure.
 6. The semiconductor structure of claim 1,wherein each inter-gate region of the shallow trench isolation structurecomprises: a pair of topmost horizontal surface segments contacting arespective bottom surface segment of a neighboring pair of gateelectrodes; and an intermediate horizontal surface segment that isadjoined to the topmost horizontal surface segments by a pair ofvertical surface segments and located between a respective pair of viacavities.
 7. The semiconductor structure of claim 6, wherein theintermediate horizontal surface segment is located above the planar topsurface of the shallow trench isolation structure.
 8. The semiconductorstructure of claim 6, wherein: bottom surfaces of the via cavities arelocated below the planar top surface of the shallow trench isolationstructure; each of the via cavities comprises a pair of stepped proximalsidewalls having a respective horizontal step located between an uppervertical proximal sidewall segment and a lower vertical proximalsidewall segment; each of the gate electrodes comprises a pair oflengthwise sidewalls that are laterally spaced apart along the firsthorizontal direction by a gate length; and a lateral spacing between apair of horizontal steps of the pair of stepped proximal sidewalls overeach inter-gate region of the shallow trench isolation structure is thesame as the gate length.
 9. The semiconductor structure of claim 1,wherein each of the gate electrodes comprises: a semiconductor gateelectrode portion contacting a top surface of a respective one of thegate dielectrics; and a metallic gate electrode portion that overliesthe semiconductor gate electrode portion.
 10. The semiconductorstructure of claim 9, wherein: the semiconductor gate electrode portioncontacts sidewalls of a pair of inter-gate regions of the shallow trenchisolation structure; the semiconductor gate electrode portion comprisesa top surface located within a same horizontal plane as topmost surfacesegments of the pair of inter-gate regions of the shallow trenchisolation structure; and the metallic gate electrode portion contactsthe topmost surface segments of the pair of inter-gate regions of theshallow trench isolation structure.
 11. The semiconductor structure ofclaim 9, wherein: lengthwise sidewalls of the metallic gate electrodeportion that are perpendicular to the first horizontal direction arevertically coincident with lengthwise sidewalls of the semiconductorgate electrode portion; widthwise sidewalls of the metallic gateelectrode portion that are parallel to the first horizontal directionare laterally offset outward from widthwise sidewalls of thesemiconductor gate electrode portion; and each inter-gate region of theshallow trench isolation structure comprises a pair of sidewall segmentsthat laterally extend along the first horizontal direction, adjoined toa respective topmost surface segment of the inter-gate region of theshallow trench isolation structure, and contacted by a sidewall of arespective one of the dielectric gate spacers.
 12. The semiconductorstructure of claim 1, wherein each dielectric gate spacer within thefirst and second field effect transistors comprises fourdownward-protruding portions vertically extending into four via cavitieswithin the shallow trench isolation structure.
 13. The semiconductorstructure of claim 1, wherein: each of the via cavities comprises a pairof first sidewalls that are parallel to the first horizontal directionand vertically coincident with widthwise sidewalls of a neighboring pairof gate electrodes, and a pair of second sidewalls that areperpendicular to the first horizontal direction and adjoined tovertically-extending edges of the pair of first sidewalls; each of thegate electrodes comprises a pair of lengthwise sidewalls that isperpendicular to the first horizontal direction and laterally spacedapart along the first horizontal direction by a gate length; and thepair of second sidewalls comprises a pair of sidewall segments that arelaterally spaced apart along the first horizontal direction by the gatelength.
 14. A field effect transistor, comprising: a semiconductoractive region including a source region, a channel region, and a drainregion arranged along a first horizontal direction; a gate dielectriccontacting a top surface of the channel region; a gate electrode havingfour sides overlying the gate dielectric; a dielectric gate spacerlaterally surrounding the gate electrode on the four sides; anddielectric offset spacers located only on two sides of the gateelectrode which extend in a second horizontal direction which isperpendicular to the first horizontal direction, wherein: the gatedielectric spacers physically contact the dielectric offset spacers overthe two sides of the gate electrode which extend in the secondhorizontal direction; and the gate dielectric spacers physically contactanother two sides of the gate electrode which extend in the firsthorizontal direction.
 15. A method of forming a semiconductor device,comprising: forming a shallow trench isolation structure in an upperregion of a semiconductor substrate that has a doping of a firstconductivity type, wherein the shallow trench isolation structurelaterally surrounds a plurality of semiconductor active regions that arepatterned portions of the semiconductor substrate, have lengthwise edgesthat are parallel to a first horizontal direction, and are laterallyspaced apart along a second horizontal direction that is perpendicularto the first horizontal direction; forming a gate strip comprising avertical stack of a plurality of gate dielectrics and a gate electrodestrip over the plurality of semiconductor active regions, wherein thegate strip continuously extends as a single continuous structure overeach of the plurality of semiconductor active regions and over portionsof the shallow trench isolation structure located between the pluralityof semiconductor active regions; forming source/drain extension regionsby implanting dopants of a second conductivity type into surfaceportions of the plurality of semiconductor active regions that are notmasked by the gate strip after formation of the gate strip; and dividingthe gate strip into the gate stacks by removing portions of the gatestrip that are located within areas of the shallow trench isolationstructure after forming the source/drain extension regions.
 16. Themethod of claim 15, wherein each of the gate stacks comprises a gatedielectric and gate electrode of a respective field effect transistor.17. The method of claim 16, further comprising: forming dielectric gatespacers around the gate stacks, wherein each neighboring pair ofdielectric gate spacers contact each other along a respective verticalplane that is parallel to the first horizontal direction; and formingdeep source/drain regions by implanting dopants of the secondconductivity into portions of the plurality of semiconductor activeregions that are not masked by the gate electrodes and the dielectricgate spacers.
 18. The method of claim 17, further comprising formingdielectric offset spacers on sidewalls of the gate strip, wherein: thegate dielectric spacers physically contact the dielectric offset spacersover the two sides of each of the gate electrodes which extend in thesecond horizontal direction; and the gate dielectric spacers physicallycontact another two sides of each of the gate electrodes which extend inthe first horizontal direction.
 19. The method of claim 17, furthercomprising: forming a patterned photoresist layer over the gate stripand the plurality of semiconductor active regions, wherein the patternedphotoresist layer comprises a row of openings arranged along the secondhorizontal direction and located within the areas of the shallow trenchisolation structure; and transferring a pattern of the row of openingsin the patterned photoresist layer through the gate strip and intounmasked areas of the shallow trench isolation structure to divide thegate strip into the gate stacks and to form a pair of via cavities thatvertically extend into the shallow trench isolation structure in eachopening within the row of openings in the patterned photoresist layer.20. The method of claim 19, wherein each of the via cavities is filledby downward-protruding portions of a respective pair of dielectric gatespacers of the dielectric gate spacers.